Flame spray powder and process

ABSTRACT

The flame spraying of the flame spray powder which has been formed by spray drying of a slip or slurry of fine particles of a flame spray material. This flame spray powder has individual particles which are of substantially spheroid shape, of a size between about 20 mesh and 1 micron, and are formed of multiple subparticles bound together without fusion by a spray-dried binder and having a crush resistance of at least 0.7 grams. For the spray drying, fine particles of any known or conventional flame spray material or combination thereof, such as metals, ceramics, carbides, etc., suspended in a slip or slurry of a liquid, preferably water, with a suitable binder and preferable auxiliary agents, is atomized into a hot drying gas stream forming the spheroid larger composite particles.

United States Patent [72] Inventor [21] Appl. No.

[22] Filed [45] Patented [73] Assignee [54] FLAME SPRAY POWDER ANDPROCESS 35 Claims, 1 Drawing Fig.

[52] U.S.Cl ll7/l05.2, 117/100, 264/12, 264/117, 75/.5,1l7/93.1 [51]Int. Cl 844d U097 [50] Field of Search 117/1052,

93.1, 100 M, 1001, 46 PS; 264/12, 13, 117, 5,6,7,

14; 75/.5, 211, .5 A, .5 AA, .5 AB, .5 B, .5 BA;

3,322,515 5/1967 Dittrich et a1 29/192 X 3,338,688 8/1967 Longoll7/l05.2 X 3,372,054 3/1968 Wishnie et al.. 75/.5 (B) X 3,373,1193/1968 Krystyniak 75/.5 UX 3,378,392 4/1968 Longo 75/.5 (B) X 3,419,41512/1968 Dittrich 117/100 Primary ExaminerAlfred L. Leavitt AssistantExaminer.lohn H. Newsome Attorney-Burgess, Dinklage and Sprung ABSTRACT:The flame spraying of the flame spray powder which has been formed byspray drying of a slip or slurry of fine particles of a flame spraymaterial. This flame spray powder has individual particles which are ofsubstantially spheroid shape, of a size between about 20 mesh and 1micron, and are formed of multiple subparticles bound together withoutfusion by a spray-dried binder and having a crush resistance of at least0.7 grams. For the spray drying, fine particles of any known orconventional flame spray material or combination thereof, such asmetals, ceramics, carbides, etc., suspended in a slip or slurry of aliquid, preferably water, with a suitable binder and preferableauxiliary agents, is atomized into a hot drying gas stream forming thespheroid larger composite particles.

FLAME SPRAY POWDER AND PROCESS This invention relates to an improvedflame spray powder, to a process for its production, and to a flamespray process utilizing the same.

Flame spraying involves the feeding of a heat-fusible material into aheating zone wherein the same is melted or at least heat-softened andthen propelled from the heating zone in a finely divided form, generallyonto a surface to be coated. The spraying is eflected utilizing a deviceknown as a flame spray gun. The material may initially be in the form ofa powder which is designated as a flame spray powder, and the gunsutilized for spraying the material initially fed in this powder form areknown as powder-type flame spray guns. In powder type flame spray guns,the flame spray powder, usually entrained in a carrier gas, is fed intothe heating zone of the gun which is most commonly formed by a flame ofsome type. The powder is either melted or at least the surface of thegrains heat-softened in this zone, and the thus thermally conditionedparticles are propelled onto a surface to provide the coating. While notrequired, a blast gas may be provided in order to aid in acceleratingthe particles and propelling them toward the surface to be coated and/orto cool the workpiece and the coating being fonned thereafter. The heatfor the heating zone while most commonly produced from a flame Tcausedby the combustion of a fuel, such as acetylene, propane, natural gas orthe like, using oxygen or air as the oxidizing agent, may also beproduced by an electric arc flame or plasma flame, or any other knownheating device.

Flame spraying in the initial stages of its commercial development wasmostly used for spraying metals and still is often referred to asmetallizing, though the same is now used for spraying a much wider groupof materials, including higher melting point or refractory metals,ceramics, cermets,

I carbides, and other metal compounds.

, A powdered heat-fusible material in order to be satisfactorillysprayed and thus considered a flame spray powder must .have certainphysical characteristics with respect to size, lphysical strength,flowability, etc. The powder must be suffrgciently flowable to be passedthrough the flame spray gun without difficulty or clogging, and thisflowability not only depends on size, absence of caking materials, suchas excess :moisture, but on shape and surface characteristics. in orderto produce a satisfactory coating the powder must have a specific {sizerange, as for example, between 20 mesh and 1 micron, |and preferablybetween 100 mesh and 3 microns, and the individual particles should notvary too greatly in their size distribution, i.e., the powder should befree of excessive fines and larger particles. The uniformity and qualityof the coating I formed by flame spraying is often dependent on theuniformity {of size of the individual particles in the powder. Duringspraying the kinetic propelling of the particles and its contact withfluid, including combustion fluids and propelling fluids, often causes aclassifying efiect which adversely affects the homogeneity anduniformity of the coating, and the presence of excess fines may changethe nature of the coating, producling for example excessive oxides orthe like.

[ in obtaining suitable commercial flame spray powders exltensivescreening and classifying techniques are generally required and only arelatively small cut of the available .jpowder material is generallysuitable for marketing as a flame spray powder. In most instancespowders are formed by reducling, as for example, milling a larger masswhich results in a 'rather wide range of particle sizes which must thenbe screened to obtain operative size range cuts. This is generally true,irrespective of the source of the mass which is milled, in-

cluding pressed, cast, calendered or extruded masses.

One object of this invention is the production of an improved flamespray powder. This and still further objects will become apparent fromthe following description read in conjunction with the drawing which isa flow sheet illustrating the process for producing powders inaccordance with the invention.

In accordance with the invention 1 have discovered that a superior andimproved flame spray powder may be produced utilizing spray dryingtechniques. In accordance with the invention finely divided flame spraymaterial suspended in a slip or slurry of liquid, preferably water, witha suitable binder and preferable auxiliary agents, is atomized and theatomized suspensiondried in a hot gas stream, forming the coarser flamespray powder, the individual particles of which are of substantiallyspheroid shape, have a size between about 20 mesh and 1 micron, and areformed of a multiple number of subparticles bound together withoutfusion by the spray dried binder, and which have a crush resistance ofat least 0.7 grams.

As the starting finely divided material utilized in the formation of theslip, any of the known or conventional flame spray materials, or anyknown combination thereof, may be used. In addition to the conventionalmetals or alloys or metal mixtures, which will ultimately form alloys orsemialloys when flame sprayed, there may be mentioned oxides, as forexample refractory oxides, such as alumina Al,0,, Beryllia BeO, CeriaCeO,, Chromia CR,O,, cobalt oxide C00, gallum oxide 021,0 hafnia l-lfO,,magnesia MgO, nickel oxide NiO, tantalum oxide TA,O thoria ThC,, TitaniaTiC,, yttrium oxide Y,O zirconia ZrC,, vanadium oxide V0, niobium oxideNbO, manganese oxide MnO, iron oxides Fe,0,, zinc oxide ZnO; complexaluminates such as BaO-Al,O,, i.e. Bao'Al O CeO'Al,O,, CoOAl,O,,Gd,O,-Al,0,, K,O-Al,0,, Li',0- Algono's A1203, Mgo'Algoa, NiO'AlgOg,srgoa'Algoa. sro'Algoa, SYO'2A1205, ZYgOa'AlgOa, ZnO-A1,0,; zit conatessuch as CaO-ZrO SrO-ZrO,, BaO'ZrO,; titanates such as A1 0 'TiO 2Ba0-Ti0CaO'TiO,, HfO,-Ti0,, 2M- gO-TiO,, SrO'TiO chromites, such as CaO-Cr,0,,ce'oc o, MgO'Cr o FeO-Cr,0,; phosphates such as A1,o,-P,0., 3BaO-PO3CaO'P O 3SrO'P O and other mixed oxides, such as La O -Fe 0;, MgO'Fe,O2MgO'GeO,, CaO-HfO,, La O -2HfO Nd O -2HfO 6BaO-Nb O Dy O -Nb O 2MgO-SnOBaO-ThO SrO-UO CaO-UO, CeO -Cr O silicates such as 3Al O.-,-2SiO(mullite), BaO-2SiO- BaO-Al O -2SiO BaO-TiO -Si0 2CaO-SiO Dy203- SiO ErO 'SiO ZrO -SiO(zircon), 2MgO-SiO ZrO-Zr- O -SiO carbides, such astitanium carbide TiC, zirconium carbide ZrC, hafnium carbide HfC,vanadium carbide VC, niobium carbide NbC, tantalum carbides TaC, Ta C,chromium carbides Cr C Cr C Cr C molybdenum carbides Mo C, MoC, tungstencarbides WC, W C, thorium carbides ThC, Th0 complex carbides, such asWC+W C, ZrC+ TiC, HfC, NbC, TaC, or VC, TiC+l-lfC, TaC, NbC, or VC;VC+NbC, TaC, or l-lfC; HfC+TaC or NbC; HbC +TaC; W WC+TaC, NbC, ZrC,TiC; WC+TiC or ZrC; TiC+Cr3C- TiC+mo C.

Borides, such as TiBg, ZrB; HfB 6mm, borides of-V, mm srm bbriaesoTTafborids'bf Cr, bbFidesofMo, borides of W, borides of the rare earthmetals;

Silicides, such as silicides of Ti eg Ti,Si

silicides of Zr eg Zr,Sr

silicides of Hf eg Hasi,

silicides of V eg V;,Si or VSi,

silicides of Nb cg Nb sr or NbSi,

silicides of TA eg Ta Si or TaSi,

silicides of Mo eg MoSi,

silicides of W eg WSi silicides of Cr eg Cr Si or Cr Si,

silicides of B eg B,Si or B, Si

silicides of the rare earth metals.

Nitrides such as boron nitrides and silicon nitrides.

Sulfides such as MgS, BaS, GrS, TiS ZrS, ZrS,, HfS, VS, V 8 CrS, M05 W8the various rare earth sulfides;

Metalloid elements, such as boron, silicon, germanium.

Cermets, such as WC/Co, W,C/Co, WC+W,C/Co, Cr/Al,0,,,.- $6 0 NiAl/Al,0,,NiAl/ZrO Co/Zr0,, Cr/Cr,C,,O Co/TiC, Ni/TiC, Co/WC-i-TiC, Cr-l-Mo/Al fNi, Fe and/or their alloys, Cu and/or its alloys such as aluminumbronze, phosphor bronze, etc., with the disulfides or deselenides of Mo,W, Nb, Ta, Ti, or V, or boron nitride for self-lubricating coatings withvery low friction coefficient.

Cermets which contain an active metal from the group composed of Ti, Zr,Ta, Cr, etc., or hydrides or other compounds or alloys of these activemetals, which will alloy with the metal phase of the cermet and promoteadhesion of the metal phase to the refractory phase by promotingwetting" of the surface of the refractory phase.

Cermets, for instance those containing a metal and a carbide as therefractory phase, which also contain free carbon, such as high puritygraphite or the like, which will effectively reduce or prevent oxidationof the carbide phase and reduce solutioning of the carbide phase in themetal binder phase.

Mixtures of any desired combinations of these or any known flame spraymaterial may be used for any purpose, including for the formation ofsynergistic composites of the type mentioned in U.S. Pat. No. 3,254,970or combinations which will exothermically react to form an intermetalliccompound as disclosed in the aforesaid patent and U.S. Pat. No.3,322,515. In addition, combinations which when flame sprayed, willendothermically react, or combinations or components which willdecompose to form desired coating materials, as for example carbonates,oxalates, nitrates or oxychlorides which will decompose to form oxidecoatings, as for instance those of thorium, zirconium, magnesium oryttrium may be used. Furthermore, mixtures of oxides and metals whichreact in a redox-type of reaction, converting a metal to an oxide and anoxide to a metal, forming metal-oxide mixtures into metaloxide orintermetallic-oxide or cermets or the like, as for instance may be used.

There also may be mentioned mixtures of metal oxides and reducingagents, metals and nonmetals, such as boron, silicon, nitrogen, sulfur,phosphorus or the like. Still further, there may be mentioned metalhydrides alone or in mixture with other materials, such as metal oxidesand the like.

These finely divided components should preferably be in the form of fineor superfine particles having, for example, a particle size below 200mesh and preferably below 325 mesh, and most preferably below microns.

These fine or superfine particles are then mechanically mixed with wateror another liquid and the binder forming a suspension which is termed aslip. The concentration of the fine or superfine particles in the slipmay vary between about 40 weight percent and 99 weight percent, andpreferably between 50 weight percent and 98 weight percent.

While water is the preferable liquid used to form the slip, due to itsready availability, low cost, nonflammability, high evaporation rate atrelatively low temperature, relative inertness and ability to dissolveor suspend useful binders, it is also possible to use other liquids,such as hydrocarbon solvents, alcohols or other organic liquids, aloneor in admixture. When using, however, flammable liquids, care must betaken to avoid combustion or explosion in the drying.

The slip must additionally contain a binder which is capable ofultimately binding the subparticles together into the flame sprayparticles of the required strength and crush resistance.-

As a binder any material which can be dissolved or suspended in themother liquid of the slip and which when dried will form a film and/oradhere to the material being agglomerated, can be used as a binderproviding that the same is sufficiently hard and tenacious to form anagglomerate of the required strength and hardness. In general,film-forming organic resins which are soluble in the liquid of the slip,may be used. Examples of these include polyvinyl alcohol, gum arabic andother natural gums, carboxy methyl cellulose salts, polyvinyl acetate,methyl cellulose, ethyl cellulose, polyvinyl butyral dispersions,protein colloids, acrylic resin emulsions, ethylene oxide polymers,water-soluble phenolics, wood extracts such as sodium, ammonium, orcalcium lignin sulfonates, sodium,

ammonium, potassium or propylene glycol alginates, various flour andstarches.

Empirically, a potential binder-material combination can be selected anda small quantity of a test slip formulated, including in the slip anyadditive required for specific purpose and compatible with the binder,i.e., wetting agent, suspending agent, deflocculents, etc., the need forwhich is determined by observation during the mixing and evaluation ofthe slip. The binder must not be precipitated from solution by anyadditive or the solid; the solids must remain reasonably well suspendedand completely dispersed in the liquid; the slip must not gel nor shouldthe solids precipitate out as a solid cake; nor should there by anyunusual chemical reaction between ingredients in the slip such as toresult in the evolution of a gas.

A qualitative measure of the effectiveness of the binder in cementingthe particles to each other can be made by drying a film of the slip ona glass microscope slide and judging the hardness abrasion resistance ofthe composite film, the adhesion of the binder to the solid particles,and, by destructively abrading the dried film gross segregation of thebinder from the solids in drying. Relative film hardness for variousbinder concentrations is very simply determined in this manner.

In addition to organic binders, inorganic binders, such as sodiumsilicate, boric acid, borax, magnesium or other soluble carbonates,nitrates, oxalates, or oxychlorides may be used.

In addition to serving strictly a binding function, binders may bechosen to perform auxiliary functions, or to impart additional desirablecharacteristics to the flame spray powder. Thus, for example, pigmentsor dyes may be added to the binder or to the slip for ultimateincorporation in the dried binder in order to permit color coding of theflame spray powder. If the flame spray material is prone to undesirableoxidation when flame sprayed, hydrocarbon binders may be chosen whichwill produce a protective inert coating or reducing atmosphere adjacentthe melting or reacting particles during the flame spraying in order tosuppress such oxidation. If it is desirable to add a further element orprevent loss of an element in the flame sprayed coating, a binder may beselected which will perform this function. Thus, a carbon-containingbinder, such as an organic binder, may be used in order to introducecarbon to form a carbide or to prevent carbon depletion in the sprayingof the carbide. Binders which will decompose to form a reducingatmosphere or containing reduction agents may be used in connection withpractically all metal or alloy components in order to reduce the oxidefilms inherently present on the subparticle surfaces and thus improveconsolidation, bonding, alloying, or reaction between constituents asthe case may be.

The binder may additionally be chosen to rapidly decompose in the flamegenerating the gas or vapor in order to, in effect, rapidly break up theagglomerated flame spray particles in the flame into a number of smallerconsolidated, fused or reacted particles, which often are desirable forproducing denser coatings. Binders may also be chosen which willdecompose in the flame to form a protective atmosphere adjacent themelting particles in order to minimize or prevent hardening ofsusceptible metals, such as molybdenum, tungsten, tantalum, or niobiumby contaminants such as oxygen, nitrogen, or carbon. Still further,binder materials which act as, or which contain, fluxes such as sodiumsilicate, boric acid, borax or the like, may be used to perform afluxing function in order to aid interparticle cohesion, adhesion to thesubstrate, and produce a superior coating of lesser porosity and higherhardness.

In the case ofspraying of oxides, such as ceramics, undesirablereduction may be prevented by including an oxidation agent, such as anitrite, nitrate, or permangenate, in the binder or in the slip fordepositing with the binder. In general, the binder material should bepresent in a concentration in the slip to form ultimate dried bindercontent in the particles of up to 10.0 weight percent, or preferably 0.1to 5.0 weight percent. For this purpose concentrations of up to 10.0weight percent, or preferably from 0.1 to 5.0 weight percent aregenerally required in the slip, based on the fine starting powdercontained in the slip.

ln addition to the fine starting powder material, the liquid and thebinder, the slip may contain auxiliary agents, such as plasticizers,wetting agents, deflocculants, suspending agents, preservatives,corrosion inhibitors, antifoam agents or defoamers, deoxidants and/oroxidizing agents when required. The use of plasticizers is preferable inconnection with binder materials which form hard, brittle films or whichmay tend to crack when drying, as for example sodiumcarboxymethylcellulose. Examples of plasticizers include glycerine,ethylene glycol, triethylene glycol, dibutyl phthalate, diglycerol,ethanolamines, propylene glycol, glycerol monochlorohydrin,polyoxyethylene aryl ether, etc. These plasticizers are generally usedin amounts of 1 weight percent to 50 weight percent and preferably 5weight percent to 30 weight percent, based on the dry binder materials.

suspending agents may be desirable to prevent premature settling of thesolids in the slip. For this purpose high molecular weight water-solublesynthetic resins or gums, as for example sodium carboxymethylcelluloseof molecular weight 200,000, methyl cellulose of molecular weight140,000, or polymers of ethylene oxide of molecular weight higher thanaround 125,000, may be used. In general, only relatively lowconcentrations ranging from a few parts per million to a few weightpercent based on the fine starting powder contained in the slip, arerequired.

Deflocculating agents may be used to aid in the slip formation and toprevent agglomeration in the slip. Examples of these include sodiumhexametaphosphate, sodium molybdate, tetrasodium pyrophosphate, ammoniumcitrate, ammonium oxalate, ammonium tartrate, ammonium chloride,monoethylamine, etc. Conventional amounts as are used in formingsuspensions and colloids may be used which, for example, may range fromzero to 1.0 weight percent, and preferably from 0.05 to 0.2 weightpercent.

Wetting agents may also be used to aid in maintaining the solidsuspension in the slip. These are the conventional synthetic detergents,such as alltylaryl sulfonates, sulfates, soaps, and the like, which maybe used in the conventional quantities, for example ranging from 1p.p.m. to 10.0 weight percent.

Certain of the binder materials may be susceptible to bacterialdegradation or mold growth during storage, in which case it may bedesirable to add a preservative to the binder material prior toincorporation in the slip, or the slip itself. Any of the known orconventional preservatives, such as sodium benzoate, phenol, or phenolderivatives, formaldehyde, merthiolate, etc. may be used in theconventional amounts and generally between about 0.1 and 0.5 weightpercent of the initial binder solution. It may be preferable to usenontoxic preservatives due to the danger of decomposition in the flame.

In connection with fine powder materials which are susceptible tocorrosion, or in connection with which the binders show a corrosiveaction, the binder should additionally contain conventionalanticorrosion agents in conventional amounts.

If the slip tends to foam during its production or during handling,conventional antifoaming agents or defoamers, may be added in theconventional amounts, as for example from 0.1 p.p.m. to 200 p.p.m.

Other miscellaneous additives may be included in the slips for specificeffects in the production or handling of the slip the slip or in theultimate flame spraying of the powder produced, as for example chemicalactivators which will aid in the sintering of high melting refractorymaterials. Thus for example chlorine or a chlorine-generating compoundmay be added to enhance the sintering of the carbides. Hydrophobicbinders may be used in connection with MgO as water vapor enhancessintering of this material. Conventional acids or bases may be added asbuffering agents to control the pH of the slip.

The slip, as mentioned, is simply formed by mechanically mixing theliquid, fine powder and the additives, with sufficient agitation to forma uniform suspension.

The slip is then pumped into a conventional spray dryer where it isatomized and spray-dried. The heavier particles recovered from thebottom of the tower are used as the flame spray powder while the smallerparticles which are also recovered from the spray drying may bereconstituted into the slip and again passed through the device.

Referring to the embodiment shown in the drawing, the slip is made up inthe mixing tank 1, as described, and pumped by the metering pump 2 tothe atomizing head 3 of the spray dryer tower 4. Atomizing air is passedinto the atomizing head 3 from the compressor 5. The slip is atomizedinto the fine spray 6. Air is pumped by the fan or ventilator 7 throughthe heater 8, as for example a conventional combustion heater, into thetop of the spray tower and passes downward as is indicated at 9, dryingthe atomized slip into the agglomerated flame spray particles which fallthe bottom of the tower and are collected in the collector to. The gasis exhausted at 11 through the cyclone separator 12, in which the finersuspended particles are separated and recovered in the collector 13.These finer particles may be reconstituted into the slip by the additionof further liquids, such as water, and repassed through the device. Thespraydryer may be operated in any of the conventional elevatedtemperatures and gas flow rates, as for example drying gas inlettemperatures between about 400 F. and 800 F. and preferably between 500F. and 700 F. In the equipment I have used, the liquid slip is generallyevaporated at a rate between 2 and l2 gallons per hour, and preferablybetween 2.5 and 8 gallons per hour, based on a drying gas outlettemperature of 225 F. to 400 F. and preferably from 250 F. to 350 F.

The flame spray powder in accordance with the invention has a generaloverall spheroid shape. Some of the spheroids are somewhat collapsed,i.e. toroidal or donut shaped, and the term spheroid" as used herein andin the claims includes this collapsed form of the spheroid, as well asother somewhat distorted spheroid shapes. These powders, as comparedwith the conventional flame spray powders, are unusually free flowingand may be handled in all of the conventional powder type flame sprayequipment without difficulty. The powder may be produced at asubstantially lower cost than was previously'possible and quitesurprisingly shows superior characteristics when sprayed, allowing forexample a higher spray rate and a substantially improved depositefficiency. The invention further allows almost unlimited possibilitiesof combining desired components into integral individual powderparticles, which was not previously possible. The combined componentparticles in accordance with the invention show many advantages over theprior art mixtures or conventional aggregates or coated powders, havinga uniform distribution of the constituents and very intimate and closecontact with each other. In the spraying process this allows completealloying, solutioning, or reacting of the components, allowing theformation of a much more homogeneous and uniform coating. When, forexample, the constituents of the composite particles are materials whichwill form a a cennet, the ceramic and other phases of a very fine sizeare uniformly distributed. Furthermore, coatings produced from the spraydried powder particles in accordance with the invention often showhigher density and abrasion resistance than those produced by theconventional powders of the same type. The unusual characteristics andflowability not only allow for better handling in the flame sprayequipment but also allow for better screening and classification inorder to obtain extremely uniform size cuts.

While the powders may generally be used as produced, with the bindersremaining soluble in the particular liquid solvent of the slip fromwhich they were formed, it is also possible to insolubilize same by acuring, cross-linking, or tanning treatment. Thus, for example theparticles may initially be treated with a dilute alcoholic solution ofchromic nitrate followed by removal of the excess solution and drying.lnsolubilization may also be effected by treatment with concentratedsolutions of dichromates, followed by exposure to actinic, such asultraviolet light. The dichromates may, for example, by any of thealkaline or metal dichromates, such as ammonium, sodiurn, potassium orcupric. lnsolubilization may also be effected by treatment with copperammonium hydroxide, as for example prepared from copper sulfate,ammonium hydroxide, and sodium hydroxide.

It is critical that the individual spray-dried powder particles inaccordance with the invention have a crush resistance of at least 0.7grams. This crush resistance is simply measure of the weight thatindividual particles will support before the same are broken, crushed ordestroyed. This crush strength is most simply determined by placing anindividual particle on anvil and detennine the maximum weight that thesame will support while remaining intact. l have found that this crushresistance can be most accurately determined with the use of ananalytical balance as follows:

The compressive strength tester is a modified analytical balance onwhich the pan on one side was replaced by an anvil atop the horizontalbeam and a counterweight, the sum weight of which exactly equalled theweight of the pan removed. A shallow depression on the upper surface ofthe anvil allows precise orientation of the particle to be tested. Anadjustable platen is mounted above and closely adjacent to the anvilsurface; the height is adjusted such that, with the particle to betested in position, the zero-indicating arm of the balance is at zero onthe reference scale when the particle is just contacting the platenface.

The load is then applied gradually and without shock by unwinding a finechain from a calibrated rotating cylinder into the other pan of thebalance, the calibrations showing the weight of chain deposited on thepan.

Compressive failure of the particle is indicated by movement of thezero-indicating arm relative to the reference scale. The weight of chainrequired to do this is directly read from the calibrated cylinder.

The particles must thus be substantially stronger and have a highercrush resistance than powders produced for most powder metallurgypurposes where the same are to be pressed into shapes or fonns.Particles, such as ceramic particles intended for initial press forming,must have a relatively low crush resistance in order to be pressed intoa green form of uniform consistency.

In addition to being sprayed per se in any of the known or conventionalmanners for flame spraying using any of the known or conventionalpowder-type flame spray equipment, the powder in accordance with theinvention may, of course, be sprayed in any desired mixture orcombination with other powder produced in accordance with the inventionor any known or conventional flame spray powder.

The following examples are given by way of illustration and notlimitation:

EXAMPLE I Tungsten Carbide'cobalt Cermet Powder Tungsten carbide (WC)powder of 1.3-1.6 micron average Fisher subsieve Size (FSS) particlesize and metallic cobalt powder of 2 micron average (FSS) particle sizewere blended in the proportion 88 weight percent WC:l2 weight percentCo. The blend of materials was then dry ball milled according tostandard practice in the industry, so that the cobalt was smeared ontothe WC particles and each WC particle was, in effect, clad with cobalt.

A gum arabic binder was dissolved in water to form a concentratedsolution containing 30 weight percent gum arabic and 70 weight percentwater. Phenol in the proportion of 0.05 weight percent, based on thetotal weight of the solution, was added as a preservative for the binderconcentrate.

Sodium carboxy methyl cellulose of very high (approximately 200,000)molecular weight was used as a suspending agent. A concentratedsolution, 1.4 weight percent of CMC and 98.6 weight percent of water,was prepared in advance.

Sodium hexametaphosphate (Calgon) was used as a dispersing anddeflocculating agent. A concentrated solution, 25 weight percent of thesolid in 75 weight percent of water, was prepared in advance.

Sodium lauryl sulfate (Proctor and Gamble Orvus WA Paste, 34 weightpercent solids in H,O) was used as a wetting agent. Because of its highefiiciency and the need in ppm. only, dilute solution was prepared bydissolving 0.3 g. of the commercial paste in 100 g. of water, resultingin a solids concentration of 0.1 g. per I00 grams of water.

A slip was formulated according to the following table, using theprepared concentrates described above, where applicable, and in theproportions indicated.

In blending the ingredients to fonn the slip, all liquids and solutionswere first weighted into the mixing tank with the mixer running. The drypowder was then fed into the mixing tank such that deflocculationoccurred immediately, and after a short mixing time, the slip wasuniform in consistency. At this point, pH was measured and adjusted topH 7.4 by buffering with phosphoric acid, and samples were taken forviscosity and specific gravity measurements. Specific gravity was 5.5g./m. Deflocculation of the powder was complete so that screening of theslip was not required. The slip was spray dried in a Laboratory TowerSpray Dryer (LT-04-l/2) as manufactured by Bowen Engineering lnc., NorthBranch, New Jersey 08856. The rated capacity of this dryer wasapproximately 20 lb./hr. of chamber product based on drying an Al,0,slip containing 60 percent to percent by weight of solids together witha suitable binder system; the chamber product consists of approximatelypercent of the total product, the remaining 25 percent being depositedin the cyclone collector and usually consists of fines. Heated air wasintroduced in a cyclonic flow pattern at the top of a verticalstraight-cylindrical drying chamber. The slip is atomized into dropletsnear the bottom of the drying chamber and directed upwards along thevertical centerline by a blast of compressed air. The particles traveltwice through the drying chamber upwards against the flow of heated airand then downward to the bottom, and then settle by gravity into acollecting receptacle.

Approximately l0,000 grams of slip were fed by pumping into theatomizing nozzle from which the atomized slip was propelled through thedrying chamber, to be finally collected in the chamber and cyclonecollectors as a dry powder. The following machine parameters were used:

Atomizing Air Flow approximately 15 SCFM Approximately 6,500 g. of the9000 g. of powder blended in the slip was collected as finished productin the chamber and cyclone collectors. The other 2500 g. was loss in themixing The cyclone product was 9 percent of the total collected and wasessentially -325 mesh size. The Hall (ASTM 8-21348 (1965)) Flow Rate ofthe l40 +325 mesh size cut of the chamber product was 2.96 gJsecond andthe apparent density (not vibrated) was 3.94 g./ml. The Hall Flow Rateof the 325 mesh cut of the chamber product was 2.99 g./second and theapparent density (not vibrated) was 3.80 g./ml. Compressive strength of60 +80 mesh particles was 10.0 grams.

A 325 mesh cut from the chamber product was flame sprayed, using a MetcoType 2M plasma flame spray gun, using argon plasma gas at lp.s.i., 100SCFH, hydrogen plasma gas at 50 p.s.i., 2.5 SCFH, and argon carriergas-at l00p.s.i., 15 SCFH. With a Type ES nozzle, input power was 500amperes at 43 volts, spray distance was 3 inches, and the spray rate was8.2 lblhour.

' The same powder was flame sprayed with the same equipment except usinga Type E nozzle and using nitrogen plasma gas at 50 p.s.i., 150 SCI-Hflow, hydrogen plasma gas at 50p.s.i., l0 SCFH flow, and nitrogencarrier gas at 50 p.s.i., l5 SCFH flow. Input power was 300 amperes at73 volts, spray distance was 3 inches, and the spray rate was 9.4lb./hr.

The same powder was flame sprayed using a Metco Type 5 P ThermoSpray gunwith a type P70 nozzle, 012 powder flow meter valve, at 4-5 spraydistance, using hydrogen at 31 p.s.i., 315 SCFH, and oxygen as thecombustion supporting and carrier gas at 31 p.s.i., 54 SCHFH. The sprayrate was 8.7 lb./hr. of powder.

In all 3 cases above, excellent, hard, dense, adherent, andwear-resistant coatings were deposited.

50 weight percent of the -l40 +325 mesh cut of the chamber product wasblended with 50 percent of a -140 +325 mesh cut of a conventionalspheroid powder of the self-fluxing, hard-facing, alloy type, to make apowder blend equal in proportion and chemistry to Metco 31C, which usesconventional cobalt-bonded tungsten carbide powder of the same chemistryand particle size range as the spray dried material. The blendedmaterial was flame sprayed, using a Metco Type 2 P ThermoSpray gun witha Type P7 nozzle, 2 powder flow meter valve, using acetylene at 10p.s.i., 25 SCFH, and oxygen at 12 p.s.i., 35 SCFH, with acetylene as thecarrier gas, and at 9.5 lb./hr. After post deposition fusing, theresultant coating was a fully fused, pore-free, homogeneous mixture ofthe coating ingredients and fully fused to the substrate.

A powder similar to that of the 31C (previous example) exceptcontaining80 weight percent of the spray dried WC/Co powder and 20 weight percentof the self-fluxing, hard-facing powder, was flame sprayed in he samemanner as in the previous example except that, after deposition of thecoating, a subsequent overcoating of the self-fluxing, hard-facing alloyalone was deposited in thickness equal to 20 percent to 25 percent ofthe first coating. The coating system was then fused, the overcoatmaterial being absorbed by the first coating during the fusing, toeffectively fill all of the pores and weld the whole to the substrate.The result was a homogenous mixture of the coating ingredients, veryhigh in WC content, and fully fused to the base.

In each of the last two spraying examples cited, the result was acoating which showed a superior grind finish, lower porosity, and equalwear-resistance and other characteristics to its conventionalcounterpart.

EXAMPLE 2 Tungsten Carbide Cobalt Cermet Powder Tungsten carbide powderof 1.3-1.6 micron average (FSS) particle size and metallic cobalt powderof 2 microns average (FSS) particle size were blended in a simplemixture, in the proportion 88 weight percent WC:l2 weight percent Co.,for incorporation in a slip as a simple mixture of powders. Thepreblending was accomplished as a convenience only in preparing powdersfor a number of experimental batches; but could be added to the slipwithout prior mixing.

The binders, suspending agents, deflocculent (dispersing agent) agent)and wetting agent, etc. were prepared for use in concentrated.solutions, the same as in example l.

A slip was fonnulated according to the following table, using theprepared concentrates where applicable, and in the proportionsindicated.

The slip was blended in the same manner as described in example Specificgravity of the slip was 3.84 g./ml.

The slip was spray dried in the same equipment and in the same manner asdescribed in example 1.

The following machine parameters were used:

Slip Feed Rate Approximately mIJmin. inlet Gas Temp. 465 F.

OutletGas Temp. 275 F.

Type Heat Direct Gas Atomizer Type Countercurrent SW Nozzle AtomizerDescription 9-028 Atomizing Air Pressure 30 p.s.i.

Atomizing Air Flow Approximately l5 SCFM Approximately 3,900 g. of the4,700 g. of powder blended in the slip was recovered as finished productin the chamber and cyclone collectors. The result was a free-flowingpowder having essentially spheroid particles. The chamber productcomprised 84 percent of the total collected and had a particle sizedistribution as follows:

Screen Size Weight Percent l5.7 t 40 es 170 +200 2.: 2o0 +230 5.5 2a0+270 3.5 -210 +325 14.5 a2s 41.5

The cyclone product comprised 16 percent of the total collected and wasessentially 325 mesh size. The Hall Flow Rate of the l40+325 mesh sizecut of the chamber product was 1.95 g./second and the apparent density(not vibrated) was 2.62 g./ml. Compressive strength of 60+80 meshparticles was 17.0 grams.

A 325 mesh cut from the chamber product was flame sprayed with the MetcoType 2M plasma flame spray gun, using the argon/hydrogen andnitrogen/hydrogen plasma gases, and with the Metco Type 5P ThermoSpraygun as described in example I. In all three cases excellent hard, dense,adherent, and wear-resistant coatings were deposited.

50/50 and 80/20 weight percent mixtures of the spray dried WC/Co powderand conventional self-fluxing, hard-facing alloy powders were blendedand flame sprayed according to the procedure described in example 1. Theresults were essentially identical. The sprayed coatings as compared toconventional sprayed coatings of the same material had smaller pores andmore uniform distribution of deposited particles and crystallites.

EXAMPLE 3 Self-Fluxing, Hard-Facing Alloy Powder The binders, suspendingagents, wetting agents, and deflocculent were prepared for use inconcentrated solutions and/or dispersions as described in example 1, orused dry. The plasticizer, glycerin, was a liquid as received.

A slip was fonnulated according to the following table, using theprepared constituents where applicable, and in the proportionsindicated. The powder" was of the following composition:

The ingredients for the slip were blended together in the mannerdescribed in example I. Specific gravity of the slip was 3.03 g./ml.

The slip was spray dried in the same equipment and in the same manner asdescribed in example I. The following machine parameters were used:

Slip Feed Rate 90 mlJminute Inlet Gas Temp. 5 l F.

Outlet Gal Temp. 300 F.

Type Heat Direct Ga:

Atomizer Type Countercurrcnt SW Nozzle Atomizer Description 9-02BAtomizing Alr Pressure 30 p.s.i.

Atomizing Air Flow Approximately SCFM Approximately l,l00 g. of the2,l00 g. of powder blended in the slip were recovered as finishedproduct in the chamber and cyclone collectors. The result was afree-flowing powder having essentially spheroid particles. The chamberproduct comprised 8 1 percent of the total product and had 'a particlesize distribution as follows:

Particle Size Weight Percent l 40 29.8 -l 40 +l 70 7.0 -l 70 +200 ll 200+2 30 5.7 -230 +270 3.9 270 +325 10.5 325 36.2

The cyclone product comprised 19 percent of the total product and wasessentially 325 mesh. The Hall Flow Rate of the l40+325 particle sizecut of the chamber product was 1.24 g./second and the apparent density(not vibrated) was 1.66 g./ml. The Hall Flow Rate of the 325 mesh cut ofthe chamber product was 0.86 g./second and the apparent density (notvibrated) was 1.68 g./ml. Compressive strength of 60+80 mesh particleswas 6.0 grams.

The l40+325 cut of the chamber product was flame sprayed, using a MetcoType 5P ThermoSpray gun with a Type P7G nozzle, 0ll powder flow metervalve, at 7 inches spray distance using acetylene as the combustible andcarrier gas at 12 p.s.i., 33 SCFl-l, and oxygen at 21 p.s.i., 60 SCFl-l.The spray 'rate was 9.2 lb./hr. After deposition of the coating on themild steel substrate, which previously had been gritblasted to improveadhesion of the as-sprayed coating, the whole was heated to aroundl,900-2,000 F to fuse the particles in the coating to each other and thecoating to the substrate. Melting and coalescence of the coating wasapparent by the formation of a layer of slag on the surface. Upon andduring cooling to room temperature, the slag layer spalled of? exposingthe bright, smooth surface of the hard, wear-resistant overlay which waswelded to the substrate.

The 325 out of the chamber product was flame sprayed the same as theprevious l40+325 cut except that a Type P7B nozzle was used and coolingair surrounded the flame of the gun. Spray rate was 7 lb./hr. Uponheating the deposited layer to around l,900-2,000 F to fuse the coatingparticles to each other and to the substrate, melting and coalescencewas apparent by the formation of a thin layer of slag on the surfacewhich coalesced into beads and permitted an excellent shine" to beobserved. The result was a smooth, even layer of a hard, weanresistantoverlay which was welded to the substrate.

The composition of the alloy fused to the substrate surface wastypically:

C0.7-l.0wt.% Crl6-l8 Si 3.5-4.5 wt. '1. Ni+Co BillflCC B 2.75-3.75 wt. bOthers 1.0 Max. Fe 3.54.5 wt. lt

EXAMPLE 4 Composite Mullite Powder Fine Mullite, 3A1,0,2Si0, can beformed into particles suitable for flame spraying by the spray dryingmethod, by agglomerating fine particles of mullite per se. lt can alsobe formed as a composite by combining available and cheap commodity rawmaterials, such as superfine molochite and high purity A1 0, in thecorrect proportion in the spray dried powder. Molochite is a naturallyoccurring mineral of the following typical composition:

SiO, 54-55 percent A1 0 42-43 percent Others 1.5-2 percent Mullite,theoretically, is 71.80 weight percent A1 0; and 28.20 weight percentSiO,. Therefore 50.8 weight percent molochite and 49.2 weight percentAlp, should result in the theoretical chemistry of mullite.

The binders, suspending agents, deflocculants, wetting agents, etc. wereprepared in concentrated solutions, the same as in example i.

A slip was formulated according to the following table, using theprepared concentrates where applicable, and in the proportionsindicated:

The slip was blended in the same manner as described in example l.Specific gravity of the slip was 1.7 g./ml.

The slip was spray dried in the same equipment and in the same manner asdescribed in example I. The following pray Guns, and with the Metco Type2M plasma flame gun. The following table lists the operating parameters:

Type 21 Type 51 Type 2M Nozzle PTC PTG EII Cnt'riet'gas Oxygen OxygenNitrogen 50/15 Oxygen pr re/llow, s H1 14/47 Acetylene pr sure/llon12/28 13/35 Nitrogen pressure/flow, 50/ (5 Hydrogen pressure/lion 50/15:Voltage r l n Ainperes .103

Spray distance. inches.

The following table compares spray rates and deposit efficiencies forspray dried composite mullite powder as compared with Metco XPl 146conventional mullite powder. The conventional material was heavilycontaminated with metal, and the spray dried mullite coatings producedwere vastly superior to the conventional mullite coatings.

Plasma flame 2M, Ell nozzle, N:/H: 3 spray distance ThermoSpray 2P, 3"spray distance ThermoSpray 51, 2" spray distance Spray Deposit SprayDeposit Sprn) Deposit rate, eiliclency rnte, eilicieney rate, ellicloncypercent #/l1r. percent #[hr percent Spray dried:

210 2.8 94 5.5 84 -230 4 V v V 5. 3 87 Conventional: XP1146 l 1.9 61

1 Deposit eflicicncy figures corrected [or hinder burnout.

machine parameters were used:

Slip Feed Rate Approximately 1 l0 mlJminute inlet (in Temperature 600'F. Outlet Gus Temperature 300' F. Type Heat Direct Gas Alomiler TypeCountercurrent SW Nozzle Atomizer Description 9-028 Atomizing AirPressure p.s.i.

The cyclone product comprised 21 percent of the total product and had aparticle size distribution as follows:

Screen Size Weight Compressive strength of 6080 mesh particles was 2.5grams.

Various particle size cuts of the chamber product were flame sprayedwith the Metco Type 2? and Type 5? ThermoS- Optimum particle size basedon the spray rates and deposit efficiencies for ThermoSpray equipment iseither 325 or 270 mesh, and for plasma flame is -230 or 270 mesh. Thepoor flowability of the conventional powder (based on spray rate forequivalent feed conditions) is also readily apparent from the data shownin the above table. With plasma flame, the spray dry spray rate was 2.8times that of the conventional material and deposit efficiency, even atthe higher rate, is L46 times that of the conventional material. Withthe ThermoS- pray 2P, feed rate was 3.2 times that of the conventionalmaterial and deposit efficiency is slightly more than twice that of theconventional material. With ThermoSpray 5P, feed rate was up to 5 timesthat of the conventional material and deposit efficiency is more thantwice that of the conventional material, even at the vastly higher sprayrate.

EXAMPLE 5 Nicket-Aluminum Exothermic Composites Nickel-aluminumcomposites corresponding to the known Metco 404 (nominally aluminum cladwith weight percent Ni) and Metco 450 powder (nominally Ni clad with 5weight percent Al) can be manufactured using this method. Ni-Al powderscontaining 5 weight percent Al and 7.5 weight per cent Al have beenmanufactured by spray drying. The spray dried composites result in theformation of an homogenous reaction product by virtue of the homogenousmixture of very fine particles.

Carbonyl nickel, 3-5 microns average particle size, and high purityspheroid Al powder, 3.5-4.5 microns, were blended in the slips in theproportion required to produce the desired composites. While the 7.5weight percent Al powder is used as a specific example, it is understoodthat the Ni:Al proportion can be anything between 99.5 weight percent Aland 0.5 weight percent Al, depending on the reaction product and theproperties desired.

The binders, suspending agents, deflocculent, wetting agent, etc., wereprepared for use in concentrated solutions, the same as in example 1.

A slip was formulated according to the following table,

using the prepared concentrates where applicable, and in the proportionsindicated:

The slip was blended in the same manner as described in example 1.Specific gravity of the slip was 2.93 g./ml.

The slip was spray dried in the same equipment and in the same manner asdescribed in example 1.

The following machine parameters were used:

Slip Feed Rate Approximately lSO ml./minute lnlet gas temperature 550'F.

Outlet gas temperature 300 F.

Type Heat Direct gas Atomizer Type Countercurrent SW Nozzle AtomizerDescription 9-02B Atomizing Air Pressure 25 p.s.i.

Atomizing Air Flow Approximately 15 SCFM Approximately 3,500 g. of the4,000 g. of powder blended in the slip were recovered as finishedproduct in the chamber and cyclone collectors. The result was afree-flowing powder having essentially spheroid particles. The chamberproduct comprised 92.5 percent of the total collected and had a particlesize distribution as follows:

Mesh Size Weight Percent The cyclone product comprised 7.5 percent ofthe total and was essentially 325 mesh.

Compressive strength of 60+80 mesh particles was 3.6 grams.

The l 7 325 cut of the chamber product was flame sprayed with a MetcoType 2P ThermoSpray gun, using a Type P7 nozzle, acetylene as thecombustible and carrier gas at 10 p.s.i., 25 SCFH, and oxygen at 12p.s.i., 35 SCFH. Spray rate was approximately 6 lb./hr. The nickel andaluminum particles in the composite particle combined exothermically inthe flame to produce an homogenous particle consisting of the nickelaluminides, the heat generated aiding in making the particlesself-bonding to the clean, smooth surface of the steel substrate. Therewas practically no smoke" produced in spraying the spray-dried powder.In the standarized Coating is sprayed on flat end of l inch diameterrod. Another rod end is bonded to the sprayed coating. Rods are pulledapart in a Universal Testing Machine, and breaking strength determined.(Metco Lab Report 0106,

-Metco lnc. I963 coating/bond strength test, the minimum bond/coatingstrength was determined as being 3,280 p.s.i., the breaking strengthwith failure occurring at the bond coattop coat interface.

EXAMPLE 6 Nickel-aluminum Exothermic Composites Example 5 was repeatedexcept that the Ni and Al were combined in the proportion 5 weightpercent A1295 weight percent Ni, with identical result.

Compressive strength of 60+ mesh particles was 3.6 grams.

EXAMPLE 7 Molybdenum Powder Molybdenum powder of less than 8 micronsmaximum, approximately 5 microns average particle size, was agglomeratedby spray drying into a powder, from which particle sizes desirable forspraying could be separated.

The binders, suspending agents, deflocculent, etc. were prepared inconcentrated solutions for use the same as in example A slip wasformulated according to the following table, using the preparedconcentrates, where applicable, and in the proportions indicated:

TABLE Total Wt. Wt. Wt. Added Addition Solids Liquid 9!:

4000 g. Molybdenum Powder 4000 g. 87.5

l33 g. Gum Arabic at 30% solids 40 g. 93 g. l 16 g. Calgon at 25% solid:4 g. 12 g. 0.l 40 g. Polyox at wt. k

solids 0.2 40 0.0"

4044.2 I45 g. 440 g. Water 585 440 g. 12.5

The slip was blended in the same manner as described in example l.Specific gravity of the slip was 4.50 g./ml.

The slip was spray dried in the same equipment and in the same manner asdescribed in example 1. The following machine parameters were used:

Slip Feed Rate ml./minute Inlet Gas Temperature 450" F.

Outlet Gas Temperature 275 F.

Type Heat Direct Gas Atomizer Type Countercurrent SW Nozzle AtomizerDescription 9-02B Atomizing Air Pressure 20 p.s.i.

Screen Size Weight Percent The cyclone product comprised 10 percent ofthe total product collected and had a particle size distribution asfollows:

Screen Size Weight Percent Trace Trace Trace Trace The Hall Flow Rate ofthe l70+325 cut of the chamber product was 2.25 g./second and theapparent density (not vibrated) was 2.8 g./ml. The 325 cut of thechamber product did not flow smoothly without vibration, so an accuratetest of the flow rate could not be made; the apparent density (notvibrated) was 2.48 g./ml.

Compressive strength of the -60+80 mesh particles was 1.3 grams.

The -170+325 cut of this and other similar molybdenum powders were flamesprayed with the Metco 2? and Metco Type 5? ThermoSpray Gun and theMetco Type 2M plasma flame gun, using spray parameters previouslydescribed.

Some of the other Mo powders manufactured using the spray dry equipmentincluded, in addition to the 1 weight percent gum arabic binder, anotherwith 1.6 weight percent gum arabic binder, one-half weight percent, 1weight percent, 2 weight percent, 3 weight percent polyvinyl alcoholbinder, and 1 weight percent sugar binder.

The following table shows spray rates and deposit efficiencies achievedwith several types of equipment flame spraying spray dried andconventional molybdenum powders:

Plasma flame 2M,

ThermoSpray 2P 2 Deposit efliclency, percent Spray rate, #lhr.

Spray rate, #/hr.

Deposit efliclency, percent Spray dried:

$4 wt. percent PVA,

1 wt. percent arable, 170 +325. Conventional: Metco #63 l Corrected forblnder burnout.

Hall flow Apparent rate of density of powder powder, g./second g./m1.

Spray Deposit efficiency,

percent Binder wt. percent PVA. 1 wt. percent PVA- 2 wt. percent PVA. 3wt. percent PVA.

EXAMPLE 8 Zirconia Powder Lime stabilized zirconia (ZIOg) Powder,containing approximately 5 weight percent of CaO to stabilize thecrystal structure in thermal cycling, of less than 10 microns maximumparticle size and approximately 3 microns average particle size, wasagglomerated by spray drying into a powder from which particle sizesdesirable for flame spraying could be separated. While the prealloyedpowder is used in this example, it is understood that the spray driedparticles could contain ZrO, plus CaO in the form of one of its manycompounds, including calcium zirconate in the correct proportion, suchthat the CaO content of the agglomerated and sprayed powder would be thedesired amount.

The binders, suspending agents, deflocculents, etc. were prepared inconcentrated solutions for use the same as in example l. A slip wasformulated according to the following table, using the preparedconcentrates where applicable, and in the proportions indicated.

Total Wt. Wt. Wt. Added Addition Solids Liquid i 3000 g. Zirconia Powder3000 g. 72 I00 g. PVA at 30% Solids 30 g. g. 1

l2 g. Calgon at 25% Solids 3 g. 9 g. 0.l

7.5 g. CMC (dry) 7.5 0.25

3040.5 79 g. H03 g. Water H82 1103 28 The slip was blended in the samemanner as described in example Specific gravity ofthe slip was 2.04g./ml.

The slip was spray dried in the same equipment and in the same manner asdescribed in example I. The following machine parameters were used:

Slip Feed Rate Approximately I50 mlJminute lnlet'Gus Temperature 500 F.

Outlet Gas Temperature 275' F.

Type Heal Direct Gas Atomizer Type Countercurrent SW Nozzle AtomizerDescription 9-025 Atomizing Air Pressure 40 p.s.i.

Screen Size Weight Percent The cyclone product comprised l9 percent ofthe total product collected and was essentially 325 mesh.

The Hall Flow Rate of the 2oo+32s cut of the chambe? product was L08g./second and the apparent density was 1.35 g./ml. (not vibrated). The325 out of the chamber product did not flow smoothly through the meterorifice of the Hall Flow Test Apparatus without vibration, so anaccurate test of the flow rate could not be made; the apparent density(not vibrated) was 1.35 g./ml.

Compressive strength of the -60+80 mesh particles was 3.5 grams.

The -200+325 and the 325 cuts of the chamber product powder were flamesprayed, using the Metco Type 2? ThermoSpray gun and with the Metco Type2M plasma flame system using spray parameters described in the previousexamples. Spray rates and deposit efiiciencies resulting from the testwork and a comparison with tests using identical equipment and sprayparameters with conventional Metco 20] (325+microns) and Metco 201B(-200+325) zirconia powders are shown in the following table:

sidered sprayable Spray rates and deposit efficiencies with spray driedpowdecomposition in flame spraying was to harden the particles of dershave been consistently better than their conventional molybdenum fromKHN 386 to KHN 549 by virtue of incounterparts where direct comparisonshave been made. In tcrsti ia containment in the molybdenum particles.addition hardness and abrasion-resistance of the spray dry powdercoatings has been consistently better. 5 EXAMPLE 13 One run each ofzirconia powder using 1 weight percent and 2 weight percent of polyvinylalcohol binder was made and Example 4 is repaated except that 3 weightPercent of flame spray tested in direct comparison with each other.Molybdate Orange When flame sprayed into water, dried andmicroscopically ex- DuPont Color based on the dry binder wasincorporated in the slip.

amined, the 2 weight percent PVA bonded powder was ob- 1o served to havesignificantly more fully fused hollow particles than the 1 weightpercent PVA bonded powder. In the preliminary coating evaluation, thecoating produced with l The results are the same except that the powderproduced is colored orange, which aided in identifying it.

weight percent PVA bonded powder was apparently denser [5 EXAMPLE andmore abrasion-resistant. In addition, with identical Ther- Example 8 isrepeated except that A1 0 with sodium silm p y yp 2P gu and p y p r ahigher deposit icate as the binder replaced the zro and the PVA BINDER.effic ency Was achieved Wlth the l Welght Percent PVA The results areessentially the same except that the sodium bonded powder: silicatedecomposed in the flame, the decomposition products p y p y includingSi0 acting to bind the A1 0 particles together. Rate Deposit RateDeposit lbJhr. Eff. lbjhr. Err.

EXAMPLE 15 2:2: :32 32:3: :3 :2: 2:: Example 8 is repeated except thatC50 with sodium carboxymethyl cellulose as the binder replaced the ZrOand the o t it td r b d b r PVA binder' EPOSI e ICIBIICIBS are COlleC t:0| in CI UI'IIOUL BIC [GU05 O ZIlCOfllfl depositedzzimniaimhepowderspmyei The compressive strength of the 60+80 mesh particles ISgreater than 0.7 grams.

The results are essentially the same.

EXAMPLE 9 EXAMPLE l6 The slip from example 1 was spray dried in a pilotplant size spray dryer as manufactured by Bowen Engineering Inc., am 15repeated except that welsh! Percent North Branch, New Jersey 08856 Therated capacity of this borosiltcate glass based on the Cr O was includedin the slip. dryer is 100 lbs/hour of chamber product based on drying anThe result fassem'auy the Same eXcFPt that the A1203 slip containing 60percent to 70 percent by weight of mate glass effectively bonded thesubpart cles of Cr,O to each solids together with a suitable bindersystem. The results were othcf durmg flame Spraymg and m "npmvmg Pamdcto the Same particle cohesion in the coating, resulting in a harder,denser,

more abrasion-resistant coating. EXAMPLE 10 40 Example 4 is repeatedexcept that the subparticles of flame EXAMPLE spray material suspendedin the slip consisted of 70 weight: Example 8 is repeated except thatNiO with methyl cellu- Percent 9f 5 mixture of 8 and 2 weight Percent ofz lose as the binder replaced the ZrO, and its binder in the slip. basedon the 8 The results are essentially identical.

Compressive strength of the 60+80 mesh powder particles is greater than0.7 grams. EXAMPLE 18 The powder is flame sprayed in the same manner asin example 4. The result is a dense, adherent, abrasion-resistantcoating consisting of essentially MgO but in which the TiO; combinedwith the MgO in the flame, permitting the deposition by enhancing themelting and coalescence of the MgO EXAMPLE l9 subparticles.

Example 8 is repeated except that CeO, replaced the ZrO, in the slip.

The results are essentially the same.

Example 8 is repeated except that TiO replaced the ZrO, in

EXAMPLE 11 the Example 7 was repeated except that 0.2 weight percent am-The results are essemlany the Same monium alginate replaced the gumarabic as the binder.

The results were essentially the same except that the am- EXAMPLE 2omonium alginate being more protective and by providing a more reducingatmosphere, the particle hardness was less by 0 approximately 100 Knoophardness because a higher purity material was deposited and particleboundary oxides in the coating were significantly reduced.

Example 2 is repeated except that boron carbide 8 C replaced thetungsten carbide and aluminum replaced the cobalt.

The results are essentially the same.

EXAMPLE 12 EXAMPLE 21 Example 11 was repeated except that 0.1 weightpercent of Example 2 is l'ePeated except that chwmillm carbide s sodiumnitrite based on the solids contained in the slip was p aced the ungstencarbide and a nickel-chrome alloy added as an oxidizing agent. pH of theslip was buffered to 7.0, replaced th o alt. using sodium hydroxidebefore the addition of the nitrite to The results are e sential y h mprevent decomposition of the nitrite and evolution of the toxic EXAMPLE22 Compressive strength of the 60+80 mesh particles was greater than 0.7grams. Example 5 is repeated except that chromium replaced the Thepowder was flame sprayed in the same manner as examnickel incorporatedin the slip in example 5.

pie 1 l. The action of the oxygen supplied by the oxidizer on its Theresults are essentially the same.

EXAMPLE 23 Example 4 was repeated except that aluminum oxide A1 andTitania TiO, replaced the solids in the slip in that example.

The results are essentially the same.

While the invention has been described in detail with reference tocertain specific embodiments, various changes and modifications whichfall within the spirit of the invention and scope of the appended claimswill become apparent to the skilled artisan. The invention is thereforeonly intended to be limited by the appended claims or their equivalentswherein I have endeavored to claim all inherent novelty.

lclaim:

l. A flame spray powder the individual particles of which are of asubstantially spheroid shape having a size between about 1 micron andminus mesh and formed of multiple subparticles bound together withoutfusion by a spray dried binder and having a crush resistance of at least0.7 grams, substantially all of said subparticles having a size of thesame order of magnitude below about 200 mesh.

2. Flame spray powder according to claim 1 having a size between about100 mesh and 3 microns.

3. Flame spray powder according to claim 1 in which said binder is awater-soluble binder.

4. Flame spray powder according to claim 3 in which said binder is anorganic polymer.

5. Flame spray powder according to claim 4 in which said binder isselected from the group consisting of polyvinyl alcohol, polyvinylacetate, gum arabic, carboxy methyl cellulose salts, methyl cellulose,ethyl cellulose, and polyvinyl butyral dispersions.

6. Flame spray powder according to claim 1 in which said subparticlesare of at least two different flame spray components.

7. Flame spray powder according to claim 6 having a size of 20 mesh and1 micron and in which said subparticles have a size below about 200mesh.

8. Flame spray powder according to claim 7 in which said binder is awater-soluble organic binder.

9. Flame spray powder according to claim 8 in which said binder isselected from the group consisting of polyvinyl alcohol, polyvinylacetate, gum arabic, carboxy methyl cellulose salts, methyl cellulose,ethyl cellulose, and polyvinyl butyral dispersions.

l0. Flame spray powder according to claim 1 in which said bindercontains a fluxing material.

11. Flame spray powder according to claim I in which said bindercontains a pigment.

12. Flame spray powder according to claim 1 in which said binder iscapable of producing a reducing atmosphere upon thermal decomposition.

13. Flame spray powder according to claim 1 in which said bindercontains an oxidizing agent.

14. Flame spray powder according to claim I in which said bindercontains a material capable of thermally combining with saidsubparticles upon flame spraying to form a flame sprayed coating.

15. Flame spray powder according to claim 1 in which said subparticlesare tungsten carbide subparticles.

l6. Flame spray powder according to claim 1 in which said subparticlesare tungsten carbide and cobalt subparticles.

l7. Flame spray powder according to claim 1 in which said subparticlesare components of a self-fluxing hard facing alloy.

18. Flame spray powder according to claim 1 in which said subparticlesare components of mullite.

l9. Flame spray powder according to claim 1 in which said subparticlesare of at least two metals capable when melted together ofexothermically reacting to form an intermetallic compound.

20. Flame spray powder according to claim 19 in which said subparticlesare nickel and aluminum subparticles.

21. Flame spray powder according to claim 1 in which said subparticlesare tungsten carbide and cobalt and said binder is sodium carboxy methylcellulose.

22. in the flame spray process in which a flame spray powder is at leastheat-softened in a heating zone and propelled onto a surface to becoated, the improvement which comprises utilizing a flame spray powderthe individual particles of which are of a substantially spheroid shapehaving a size between about 1 micron and minus 20 mesh, and formed ofmultiple subparticles bound together without fusion by a spray-driedbinder and having a crush resistance of at least 0.7 grams.

23. Improvement according to claim 22 in which said binder is an organicwater-soluble binder.

24. Improvement accordin to claim 22 in which said subparticles are ofat least two di erent flame spray components.

25. improvement according to claim 24 in which said components are metalwhich exothermically react together at the temperature in the heatingzone forming an intermetallic compound.

26. improvement according to claim 22 in which said binder containsmaterial capable of combining with the subparticles at the temperaturein the heating zone to form the flame sprayed coating.

27. Improvement according to claim 22 in which said subparticles areselected from the group consisting of tungsten carbide with cobalt ormolybdenum and in which said binder is selected from the groupconsisting of carboxy methyl cellulose and polyvinyl alcohol.

28. A process which comprises spray drying a slip containing fineparticles of a flame spray material and a binder to form spray-driedaggregate particles having a crush resistance in excess of about 0.7gram, passing these spray-dried particles into a heating zone, heatingthe particles to at least heat-soi tened condition in the zone andpropelling the heated particles onto a surface to form a coating.

29. Process according to claim 28 in which said slip is an aqueous slipcontaining an organic water-soluble binder.

30. Process according to claim 29 in which said organic binder is amember selected from the group consisting of polyvinyl alcohol,polyvinyl acetate, gum arabic, carboxy methyl cellulose salts, methylcellulose, ethyl cellulose, and polyvinyl butyral dispersions.

31. Process according to claim 28 in which said subparticles have aparticle size below 200 mesh.

32. Process according to claim 28 in which said slip contains finesparticles of at least two different flame s ray materials.

3 Process according to claim 32 in w rch sald two different flame spraymaterials are materials capable of exothermically reacting with eachother at the temperature in the heating zone to form an intermetalliccompound.

34. Process according to claim 28 in which the slip additionallycontains a material capable of thermally combining with the flame spraymaterial to form a flame sprayed coating.

35. Process according to claim 28 in which said fine particles of flamespray material are tungsten carbide and cobalt, and said binder issodium carboxy methyl cellulose.

2. Flame spray powder according to claim 1 having a size between about100 mesh and 3 microns.
 3. Flame spray powder according to claim 1 inwhich said binder is a water-soluble binder.
 4. Flame spray powderaccording to claim 3 in which said binder is an organic polymer. 5.Flame spray powder according to claim 4 in which said binder is selectedfrom the group consisting of polyvinyl alcohol, polyvinyl acetate, gumarabic, carboxy methyl cellulose salts, methyl cellulose, ethylcellulose, and polyvinyl butyral dispersions.
 6. Flame spray powderaccording to claim 1 in which said subparticles are of at least twodifferent flame spray components.
 7. Flame spray powder according toclaim 6 having a size of 20 mesh and 1 micron and in which saidsubparticles have a size below about 200 mesh.
 8. Flame spray powderaccording to claim 7 in which said binder is a water-soluble organicbinder.
 9. Flame spray powder according to claim 8 in which said binderis selected from the group consisting of polyvinyl alcohol, polyvinylacetate, gum arabic, carboxy methyl cellulose salts, methyl cellulose,ethyl cellulose, and polyvinyl butyral dispersions.
 10. Flame spraypowder according to claim 1 in which said binder contains a fluxingmaterial.
 11. Flame spray powder according to claim 1 in which saidbinder contains a pigment.
 12. Flame spray powder according to claim 1in which said binder is capable of producing a reducing atmosphere uponthermal decomposition.
 13. Flame spray powder according to claim 1 inwhich said binder contains an oxidizing agent.
 14. Flame spray powderaccording to claim 1 in which said binder contains a material capable ofthermally combining with said subparticles upon flame spraying to form aflame sprayed coating.
 15. Flame spray powder according to claim 1 inwhich said subparticles are tungsten carbide subparticles.
 16. Flamespray powder according to claim 1 in which said subparticles aretungsten carbide and cobalt subparticles.
 17. Flame spray powderaccording to claim 1 in which said subparticles are components of aself-fluxing hard facing alloy.
 18. Flame spray powder according toclaim 1 in which said subparticles are components of mullite.
 19. Flamespray powder according to claim 1 in which said subparticles are of atleast two metals capable when melted together of exothermically reactingto form an intermetallic compound.
 20. Flame spray powder according toclaim 19 in which said subparticles are nickel and aluminumsubparticles.
 21. Flame spray powder according to claim 1 in which saidsubparticles are tungsten carbide and cobalt and said binder is sodiumcarboxy methyl cellulose.
 22. In the flame spray process in which aflame spray powder is at least heat-softened in a heating zone andpropelled onto a surface to be coated, the improvement which comprisesutilizing a flame spray powder the individual particles of which are ofa substantially spheroid shape having a size between about 1 micron andminus 20 mesh, and formed of multiple subparticles bound togetherwithout fusion by a spray-dried binder and having a crush resistance ofat least 0.7 grams.
 23. ImpRovement according to claim 22 in which saidbinder is an organic water-soluble binder.
 24. Improvement according toclaim 22 in which said subparticles are of at least two different flamespray components.
 25. Improvement according to claim 24 in which saidcomponents are metal which exothermically react together at thetemperature in the heating zone forming an intermetallic compound. 26.Improvement according to claim 22 in which said binder contains materialcapable of combining with the subparticles at the temperature in theheating zone to form the flame sprayed coating.
 27. Improvementaccording to claim 22 in which said subparticles are selected from thegroup consisting of tungsten carbide with cobalt or molybdenum and inwhich said binder is selected from the group consisting of carboxymethyl cellulose and polyvinyl alcohol.
 28. A process which comprisesspray drying a slip containing fine particles of a flame spray materialand a binder to form spray-dried aggregate particles having a crushresistance in excess of about 0.7 gram, passing these spray-driedparticles into a heating zone, heating the particles to at leastheat-softened condition in the zone and propelling the heated particlesonto a surface to form a coating.
 29. Process according to claim 28 inwhich said slip is an aqueous slip containing an organic water-solublebinder.
 30. Process according to claim 29 in which said organic binderis a member selected from the group consisting of polyvinyl alcohol,polyvinyl acetate, gum arabic, carboxy methyl cellulose salts, methylcellulose, ethyl cellulose, and polyvinyl butyral dispersions. 31.Process according to claim 28 in which said subparticles have a particlesize below 200 mesh.
 32. Process according to claim 28 in which saidslip contains fine particles of at least two different flame spraymaterials.
 33. Process according to claim 32 in which said two differentflame spray materials are materials capable of exothermically reactingwith each other at the temperature in the heating zone to form anintermetallic compound.
 34. Process according to claim 28 in which theslip additionally contains a material capable of thermally combiningwith the flame spray material to form a flame sprayed coating. 35.Process according to claim 28 in which said fine particles of flamespray material are tungsten carbide and cobalt, and said binder issodium carboxy methyl cellulose.